Illicit drug use is common among young adults. Among 18-34 year olds in the general population, nearly as many report past-year use of an illicit drug (30-34%) as report "at-risk" levels of drinking (30-44%), and fewer than half of these qualify as having either an abuse or dependence diagnosis. National policy initiatives for Screening, Brief Intervention and Referral (SBIR), representing a $108.5 million federal investment, presently target both drug and alcohol use. However, evidence-based consensus bodies endorse such interventions only for at-risk drinking, and have reported that the evidence remains insufficient to support such interventions in regard to drug use in the general population. Closing this troubling gap between evidence and federal policy will require a demonstration that drug use among adults in the general population is associated with worse health and service outcomes, and that alterations in use are associated with changes in these outcomes. To date, health outcomes data have principally been accrued from clinical samples of persons with addictions and may not be informative for persons in the general population seen in primary care. We therefore propose to close this evidentiary gap through the analysis of a geographically and racially-diverse 20-year prospective community-based cohort of adults enrolled in the Coronary Artery Risk Development in Young Adults (CARDIA) study. These 5115 healthy young adults were 18-30 years old when recruited in 1985/86 and have undergone repeated in-person examinations as well as detailed psychosocial assessments since that time. Drug and alcohol use in CARDIA are comparable in prevalence to contemporaneous national samples. We propose analysis of CARDIA's existing data to: (1) Characterize associations between drug use trajectories in young adulthood and health outcomes in middle age (ages 40-52), and (2) Characterize associations between drug use trajectories in young adulthood and health service utilization in middle age, including hospitalization and access to primary medical care. Hypotheses-driven analyses will consider associations between the trajectories of marijuana and nonmarijuana drugs and general health outcomes (mortality, health-related quality of life, and count of medical conditions);specific health outcomes for particular drugs (hypertension in relation to cocaine, pulmonary function decline in relation to marijuana);and health service utilization (hospitalization, emergency department utilization, and access to primary care.) The large size of this cohort, and the prospective collection of detailed drug, health, health service and psychosocial data make CARDIA uniquely well-suited for this purpose. Because drug use changes over the life-course, a key innovation for the present application is the application of group-based trajectory analysis to optimally capture the dynamic character of drug use over time.